Metal bonded refractory



2,986,807 METAL BONDED REFRACTORY Jerome K. Elbaum, Kokomo, Ind., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed Sept. 3, 1958, Ser. No. 758,685 4 Claims. (Cl. 29-1828) This invention relates to a metal-bonded refractory and to a process for producing the same and, more particularly, to a metal-bonded tungsten carbide article and to a process for producing the same.

Tungsten carbide has many applications in industry, for example, tungsten carbide has been used in dies for drawing, in tools for facing and as wear-resistant parts for valve seats. In many of these industrial applications, tungsten carbide has been bonded with cobalt or other metals. Cobalt-bonded tungsten carbide is very hard and is, therefore, resistant to erosion and abrasion; however, this material is unable to withstand extremely corrosive conditions. For example, in a coal hydrogenation process, the extremely corrosive conditions result in a leaching of the metallic binder. This necessarily results in a weak structure which wears very rapidly. For this reason, it may be seen that there is a need for a metal-bonded tungsten carbide that is not only erosion and abrasion resistant, but also corrosion resistant.

Accordingly, it is the primary object of the invention to provide a corrosion resistant metal-bonded tungsten carbide article.

Another object of the invention is to provide a corrosion resistant metal-bonded tungsten carbide demonstrating increased transverse break strength.

Still another object of the invention is to provide a process for the production of metal-bonded tungsten carbide having the above-mentioned properties.

Other aims and advantages of the present invention will be apparent from the following description and appended claims.

In accordance with the present invention, a process for the production of a corrosion resistant metal-bonded refractory is provided comprising sintering a finely-divided mixture having a maximum particle size up to about 150 mesh, the finely-divided mixture comprising between about 70 and 92 weight percent tungsten carbide and between about 8 and 30 weight percent binder, said binder consisting of pre-alloyed cobalt-base alloy containing between about 28 and 30 weight percent chromium, between about 3 and 6 weight percent tungsten, between about 0.8 and 1.5 weight percent carbon, and the remainder substantially all cobalt.

It has been found that, in order to produce a corrosion resistant metal-bonded tungsten carbide and to develop the properties of the metal-bonded tungsten carbide to their maximum, it is necessary that the tungsten carbide and binder be reduced to a maximum particle size up to about 150 mesh and preferably to a maximum particle size of about 270 mesh. This reduction in particle size assures more intimate mixing of the constituents, requires less heat of fusion during sinten'ng operations and provides a stronger bond between the constituents. Any conventional method for the reducing particle size may be used. All mesh sizes hereinafter referred to are mesh sizes corresponding to the US. Screen Series.

The tungsten carbide of the invention is bonded with a pre-alloyed cobalt-base alloy. It has been found that, the use of a pre-alloyed cobalt-base alloy as a binder, not only imparts the desired corrosion resistance to the bonded tungsten carbide, but also appreciably enhances the transverse break strength of the bonded tungsten carbide at standard temperature conditions. Tungsten carbide comprises between about 70 and 92 weight percent of Patented June 6, 1961 2 this composition and the binder consisting of a pre-alloycd cobalt-base alloy comprises between about 8 and 30 weight percent of this composition. Preferably, however, tungsten carbide comprises between about 76 and 86 weight percent of this composition and the binder consisting of cobalt-base alloy comprises between about 14 and 24 weight percent of the composition. The pre-alloyed cobalt-base alloy contains between about 28 and 30 weight percent chromium, between about 3 and 6 weight percent tungsten, between about 0.8 and 1.5 weight percent carbon, and the remainder substantially all cobalt.

It has also been found that a further significant increase in the transverse break strength of the metal-bonded tungsten carbide of the invention can be obtained without adversely efifecting the corrosion resistance of the composition by employing a binder consisting essentially of a pre-alloyed cobalt-base alloy and minor but significant amounts of cobalt metal. However, in order to produce a corrosion resistant metal-bonded tungsten carbide cornposition with the addition of cobalt metal to the binder, it is essential that the amount of cobalt metal does not exceed the amount of pre-alloyed cobalt-base alloy in the binder. In this form of the invention, tungsten carbide comprises between about 70 and 92 weight percent of the composition and the binder, consisting essentially of pre alloyed cobalt-base alloy and cobalt metal comprises between about 8 and 30 weight percent of the composition with the cobalt metal comprising between about 4 and 15 Weight percent of the composition. Preferably, however, tungsten carbide comprises between about 76 and 86 weight percent of the composition and the binder, consisting essentially of pre-alloyed cobalt-base alloy and cobalt metal, comprises between about 14 and 24 weight percent of the composition with the cobalt metal comprising between about 7and 12 weight percent of the composition. The cobalt-base alloy employed has the same composition as heretofore described.

The tungsten carbide and binder of the invention are bonded by sintering. The sintering operation may be performed by a combination of pressing and heating, either simultaneously or sequentially. When corrosion resistant tungsten carbide is prepared with a binder consisting of pre-alloyed cobalt-base alloy by simultaneously pressing and heating, it has been found that, by the use of certain prescribed temperature and pressure conditions, the physical properties of the materials are developed to a maximum. In this operation, the pressure employed is between about 1500 and 2000 pounds per square inch and the temperature is between about 2300 F. and 2600 F. When corrosion resistant tungsten carbide is prepared with a binder consisting of pre-alloyed cobalt-base alloy by pressing and subsequently heating, it has been found that the pressure employed is between about 20,000 and 36,000 pounds per square inch and the temperature is between about 2000 F. and 2400 F.

In preparing a corrosion resistant metal-bonded tungsten carbide with a binder consisting essentially of prealloyed cobalt-base alloy and cobalt metal b-y simultaneously pressing and heating, it has been found that pressure employed is between about 1500 and 2000 pounds per square inch and the temperature is between about 2400 F. and 2750 F. When corrosion resistant metalbonded tungsten carbide is prepared with a binder consisting of pre-alloyed cobalt base alloy and cobalt metal by pressing and subsequent heating, it has been found that the pressure employed is between about 20,000 and 36,000 pounds per square inch and the temperature is between about 2200 F. and 2700" F.

The metal-bonded tungsten carbide of the invention demonstrates a degree of corrosion resistance not heretofore found in metal-bonded refractories. For example, valves made from materials, such as chromium carbide and nickel, titanium carbide and nickel and metal-bonded tungsten carbides, were used in a coal hydrogenation process. The extremely corrosive conditions in the coal hydrogenation process conclusively proved that these ma terials did not possess the proper combination of physical and mechanical properties to be of value for this use. The acid slurry rapidly leached out the binder in the metal-bonded refractories, thus resulting in a structure no longer suitable for use.

Articles of manufacture, such as sleeves, bearings and valves, were produced from the metal-bonded tungsten carbide of this invention. The valves produced were used in a coal hydrogenation process at a pressure and temperature of about 5500 psi. and 1000 F., respectively. The metal-bonded tungsten carbide of the invention showed no noticeable defects after 300 hours, while the metal-bonded refractories heretofore discussed showed noticeable defects, such as erosion and leaching out of the binder, after about 72 hours.

The improved physical and mechanical properties of the bonded tungsten carbide of the invention may be seen from Table I below:

Table I TUNGSTEN CARBIDE BONDED WITH COBALT-BASE ALLOY Cobalt-Base Density, Hardness, Modulus of Tungsten Carbide Alloy (Weight Gin/cc. Rockwell Rupture,

Percent) A p.s.i.

TUNGSTEN CARBIDE BONDED WITH PRE-ALLOYED COBALT-BASE ALLOY AND COBALT C0balt-Base Cobalt Hardness, Modulus of Tungsten Carbide Alloy (Weight (Weight Rockwell Rupture,

Percent) Percent) A psi.

All modulus of rupture (transverse break strength) determinations were made on a one-half inch square bar resting on a two-inch span.

In an example of the invention, 80 weight percent or tungsten carbide and weight percent of cobalt-base alloy were intimately mixed. These materials .were simultaneously pressed and heated. The pressure employed was 2000 pounds per square inch andthe temperature was 2375 F. This temperature and pressure were maintained for about one-half hour. Subsequently, the mechanical properties of the metal-bonded tungsten carbide were measured. The results of these measurements are as set forth in Table II below:

Table II Hardness, Rockwell A: Modulus of rupture, p.s.i. 92 144,000

In another example of the present invention, 76 weight Table III Modulus of rupture, p.s.i. 250,000

Hardness, Rockwell A:

What is claimed is:

l. A corrosion raistant metal-bonded refractory comprising between about and 92 weight percent tungsten carbide and between about 8 and 30 weight percent binder, said binder consisting of pro-alloyed cobalt-base alloy containing between about. 28 and 30 weight percent chromium, between about 3 and 6 weight percent tungsten, between about 0.8 and 1.5 weight percent carbon, and the remainder substantially. all cobalt.

2. A corrosion resistant metal-bonded refractory comprising between about 76 and 86 weight percent tungsten carbide and between about 14 and 24 weight percent binder, said binder consisting of pro-alloyed cobalt-base alloy containing between about 28 and 30 weight percent chromium, between about 3 and 6 weight percent tungsten, between about 0.8 and 1.5 weight percent carbon, and the remainder substantially all cobalt.

3. A corrosion resistant metal-bonded refractory. comprising between about 70 and 92 weight percent tungsten carbide, between about 8 and 30 weight percent binder consisting essentially-of pre-alloyed cobalt-base alloy and cobalt metal, said cobalt metal comprising between about 4 and 15 weight percent of the composition, said cobalt-base alloy containing between about 28 and 30 weight percent chromium, between about 3.and 6 weight percent tungsten, between about 0.8 and 1.5 carbon, and the remainder substantially all cobalt.

4. A corrosion resistant metal-bonded refractory comprising between 76 and 86 weight percent tungsten carbide, between about 14 and 24 weight percent binder, said binder consisting essentially of pre-alloyed cobaltbase alloy and cobalt metal, said cobalt metal comprising between about 7 and 12 weight percent of the composition, said cobalt-base alloy containing between about 28 and 30 weight percent chromium, between about 3 and 6 weight percent tungsten, between about 0.8 and 1.5 weight percent carbon, and the remainder substantially all cobalt.

References Cited in the file of this patent UNITED STATES PATENTS 2,349,052 Ollier May 16, 1944 OTHER REFERENCES Simons Jan. 14, 1941 

1. A CORROSION RESISTANT METAL-BONDED REFRACTORY COMPRISING BETWEEN ABOUT 70 AND 92 WEIGHT PERCENT TUNGSTEN CARBIDE AND BETWEEN ABOUT 8 AND 30 WEIGHT PERCENT BINDER, SAID BINDER CONSISTING OF PRE-ALLOYED COBALT-BASE ALLOY CONTAINING BETWEEN ABOUT 28 AND 30 WEIGHT PERCENT CHROMIUM, BETWEEN ABOUT 3 AND 6 WEIGHT PERCENT TUNGSTEN, BETWEEN ABOUT 0.8 AND 1.5 WEIGHT PERCENT CARBON, AND THE REMAINDER SUBSTANTIALLY ALL COBALT. 